Assessment and Future Directions of Nonlinear Model Predictive ...

384 K. Naidoo et al.polymer control projects should be executed, what practical issues have to befaced, and to describe the solutions that have been adopted.This paper starts with a brief description of some example industrial processesthat will be referred to later in the paper. The remaining sections in thepaper outline, in chronological order, the various phases of deploying one ofthese solutions. At each stage, technological and practical points of interest arediscussed.2 Process DescriptionsIn this section we will briefly describe some typical polymer processes, whichwill serve to illuminate some of the later discussion. In the interests of space,we will limit the discussion to two specific polymer processes, but much of thediscussion is common to a wide range of continuous polymer manufacturing technologieson which Aspen Technology has implemented nonlinear MPC, includingDow UNIPOL Polyethylene (PE) and Polypropylene (PP), Basell SpheripolPolypropylene (PP), Polystyrene, BP Innovene PE and PP, and High PressureTube Low Density Polyethylene (LDPE).2.1 Dow UNIPOL PolyPropyleneThe Dow UNIPOL PP process is a gas phase, dual series reactor process capableof making impact and random copolymer and homopolymer grades. The processconsists of several sections including Raw Material Purification, Reactors, Resindegassing, Vent Recovery, Pelletizer, Blending and Bagging, Compounding, etc.MPC is usually applied to the reaction and related systems, but can be extendedto the vent recovery unit. Figure 1 shows a schematic of the first reactor section.On the reactors, there are both quality and composition variables requiringcontrol. Quality variables relate to the powder properties, while compositionFig. 1. First Reactor Section of Dow’s UNIPOL PP Process